refactor(ext): broaden required-pill test + drop dead .label .req CSS

Code-review feedback on Task 4:
- Test expanded from login-only to it.each across all 7 type forms
  (14 assertions total). A future revert to <span class="req">*</span>
  in any form now fails CI.
- .label .req rule removed from popup/styles.css and vault/vault.css —
  zero consumers after the REQUIRED_PILL_HTML migration.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

extension/src/popup/styles.css

@@ -81,12 +81,6 @@ body {
   margin-bottom: 4px;
 }
 
-.label .req {
-  color: var(--accent-strong);
-  margin-left: 2px;
-  font-weight: 600;
-}
-
 .req-pill {
   display: inline-block;
   font-size: 9px;